Heat-exchanger trays and system using same

ABSTRACT

A novel distillation tray useful as a horizontally disposed internal for a distillation column, especially a cryogenic distillation column, has a set of parallel horizontal pipes spaced from one another to support a pool of down-flowing liquid and to provide passage of up-flowing vapor through the spaces. At each end the pipes are connected to and communicate with a manifold. A number of these trays in a vertically tiered array are connected to one another as an assembly in the column. The assembly of the trays is provided by the manifolds at the two ends of the sets of pipes. In one construction the manifold for one set of pipes has an upward vertical extension that is also one manifold of the adjacent upper tray, while the other manifold for the first set of pipes has a downward vertical extension that is also one manifold of the adjacent lower tray. In another construction the manifold at one end of a set of pipes is connected to a pipe extending upwardly to the manifold of the adjacent upper tray, while the manifold at the other end is connected to the pipe that extends upwardly from the manifold at that end of the adjacent lower tray. The manifold of the lowermost tray that is not in communication with the manifold of the tray immediately above it is connected to a pipe extending through the wall of the column. The manifold of the uppermost tray of such assembly that is not in communication with a manifold of the tray below it is connected to a pipe extending through the column wall. Alternatively, that uppermost manifold has an opening to the chamber of the column so that fluid after passage through the assembly of trays is then introduced directly into the column as a feed for the column. As a second alternative, the set of pipes of the top tray of the assembly in the stripping section of a column can be short to feed the fluid to the chamber of the column. Columns containing the assembly of the trays in the stripping section and/or rectifying section are especially useful in novel distillation systems.

This is a division of application Ser. No. 415,524, filed Nov. 14, 1973,now U.S. Pat. No. 3,969,450.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to distillation column internals, particularlydistillation trays and an assembly of such trays, to distillation columnincluding such trays, and to systems utilizing such distillationcolumns. This invention is directed to a specific construction ofdistillation trays and an assembly of these trays that, when mounted ina distillation column, provide indirect heat exchange of a fluid withliquid and vapor in the chamber of the distillation column.

2. Description of the Prior Art

The principles and design procedures of distillation to separate amaterial containing two or more component by boiling the material inliquid form are described in my book entitled "Distillation" publishedin 1961 by Reinhold Publishing Corporation, New York, N. Y. One of thechapters of the book is directed particularly to column internalsincluding distillation trays. Of the various types of trays of the priorart described in that chamber the most pertinent type of trays isTurbogrid trays that have long narrow slots that could be considered asmodified sieve trays. Sieve trays are merely plates perforated withsmall holes. The Turbogrid trays are made either by stamping slots outof a flat metal plate or by the use of parallel metal bars or slatsspaced from one another to provide many long narrow slots for each tray.

As described also in my book mentioned above, there are two types ofdistillation trays broadly speaking. These are refered to as cross-flowtrays and shower-type trays. The former type has a downcomer thatcarries the liquid to the next lower tray. That liquid flows across thetray and then over a weir to the downcomer. Turbogrid trays arerecommended for use as shower-type trays, although they could be usedwith downcomers. An assembly of vertically tiered distillation trays aredisposed within the rectifying section of a distillation column andanother assembly of such trays are disposed in the stripping section ofthe column. The liquid feed is introduced into the column between thesetwo sections.

As mentioned above, the special utility of the invention is in the fieldof cryogenic distillation, particularly low-temperature distillation ofa product from the steam-cracking of light hydrocarbons, to separateethylene from other components in the cracked gaseous product. Adescription of low-temperature processing of such cracked gases ispresented in the 1946 article entitled "Low Temperature Processing ofLight Hydrocarbons" by A. W. Pratt and N. L. Foskett in Transactions ofAmerican Institute of Chemical Engineers, vol. 42, pages 149-163. Withrespect to the systems of the present invention, other relevantpublications include: the article entitled "Cracked-gas quenching,compression" by S. B. Zdonik et al. The Oil and Gas Journal, Nov. 24,1969, at pages 96-101; the article entitled "Low-pressuredemethanization techniques for ethylene plants" by W. K. Lam et al. inThe Oil and Gas Journal, May 18, 1970, beginning at page 111; thearticle entitled "Cryogenic gas-processing plant goes on stream in WestVirginia" appearing in the Nov. 24, 1969, issue of The Oil and GasJournal at pages 81-83; and the article entitled "New Flow Sequence forEthylene Plants" in Hydrocarbon Processing, June, 1970, at page 13. Withrespect to one of the systems of the present invention, one system ofthe prior art that is generally relevant is U.S. Pat. No. 3,444,696. Innone of the prior art including the articles and patent mentioned aboveis there any disclosure of a distillation tray that is constructed tofunction also for a heat exchange between liquid and vapor in the columnwith liquid passing through an assembly of such trays.

SUMMARY OF THE INVENTION

The distillation tray of the invention is referred to hereinafter as aheat-exchanger tray because it also functions to transfer thermal energybetween fluid, usually liquid as described below, inside the tray andliquid and vapor outside the tray but within the chamber of thedistillation column. The heat-exchanger tray of the invention isconstructed to provide the indirect heat exchange with fluid inside thetray flowing transversely of the general direction of flow of the liquidand the vapor in the chamber of the distillation column.

The heat-exchanger tray of the present invention includes a set ofparallel horizontal pipes and two manifolds connected to andcommunicating with opposite ends of the set of pipes and having anotheropening for each. For intermediate trays these other openings facevertically in opposite directions. For each of the top and bottom traysof an assembly only one of the other openings faces the adjacent tray.Usually the other opening is located to connect to a pipe pg,5 throughthe wall of the column. For a system in which liquid feed to the chamberof the column is first passed through an assembly in a stripping sectionthat top manifold has an opening that communicates with the chamber ofthe column.

The heat-exchanger tray of the invention has its set of parallelhorizontal pipes spaced from one another a short enough distance so thatthe set of pipes will hold a pool of down-flowing liquid through whichup-flowing vapor passes after passing through the spaces between thepipes. The heat-exchanger trays of the invention can be constructed sothat these spacings are such that the trays function as cross-flow traysor can be constructed so that the trays function as shower-type trays.

When constructed to function as cross-flow trays the liquid in thechamber held as a pool above each tray flows across the tray and over aweir and then downwardly through a downcomer and past a weir to the traybelow. This flow is a horizontal flow that is preferably transverse tothe axis of the pipes of the set. This pool is fed with liquid thatflows across a heat-exchanger tray above that tray and then flows over aweir and through a downcomer. The construction of inlet weirs and exitweirs for the tray and the downcomers is basically their constructionfor columns using conventional cross-flow trays.

When the heat-exchanger tray of the invention is constructed as ashower-type tray the space between the pipes of the set of pipes of thetray is such that the liquid in the chamber flows down through theopenings between the pipes, while at the same time the vapor flowsupwardly through these openings. Of course, in this case as withconventional shower-type trays downcomers and weirs are not present.

In one embodiment of the heat-exchanger tray the two manifolds are tubesand their other, usually oppositely facing, vertical openings arelocated generally centrally of the length of the tubular manifold. Whenusing this embodiment a number of these trays are placed in avertically-tiered, spaced arrangement as an assembly of heat-exchangertrays. In this assembly of a number of vertically spaced heat-exchangertrays the intermediate trays have, at their oppositely facing openingsof their manifolds, tubes connecting those manifolds to similar openingsin manifolds of adjacent heat-exchanger trays. The top and bottomheat-exchanger trays of the assembly have only one of their manifoldswith the generally central opening facing a similar opening in amanifold of an adjacent heat-exchanger tray, as stated above. A tube ismounted at that opening to connect that opening to the adjacentintermediate heat-exchanger tray. The other manifold of the bottomheat-exchanger tray of the assembly is connected to a pipe that extendsthrough the wall of the distillation column. The other manifold of thetop heat-exchanger tray can be connected to a pipe that extends throughthe wall of the distillation column.

Alternatively, that other manifold of the top heat-exchanger tray is notconnected to a pipe extending through the wall of the column so that thefluid passing through the assembly of heat-exchanger trays flowsdirectly into the chamber from one or more openings in that manifold.The alternative construction is used, as mentioned earlier in connectionwith a broader statement regarding the trays, when the assembly is anassembly in the stripping section of a distillation column for a systemin which the liquid feed to the chamber of the column is to be furtherlowered in temperature prior to its introduction to the central portionof the chamber of the column. For this system the top tray can beconstructed without that manifold. Alternatively, the pipes of the toptray can be shorter so that they are used merely to provide multipleintroduction of the feed from the assembly to the chamber at thatelevation. In that case the exit manifold is not present.

In another embodiment of the heat-exchanger tray a number of the traysare formed in which several sets of pipes are disposed in avertically-tiered, spaced array. In this array one end of the severaladjacent sets of horizontal pipes are connected to a manifold so thatthe manifold communicates with that end of all of those sets of pipes.That manifold extends upwardly from this array and has other openings tocommunicate with one end of several other adjacent sets of horizontalpipes connected to that manifold and disposed in a vertically-tiered,spaced array above and spaced from the first array. The other end of thesets of pipes of the first array of pipes is similarly connected to atop portion of another manifold having sets of openings communicatingwith those ends of the sets of pipes at different elevations. The lattermanifold has a downward extension that has holes similarly disposed tocommunicate with one end of another array of sets of pipes that areconnected at their other end to the top portion of another manifold.This construction is repeated at both ends of the arrays of pipes sothat the overall assembly has many arrays of pipes that are in avertically tiered or stacked arrangement and that communicate with setsof manifolds that are vertically tiered and that have ends of pipesconnected to them. The overall assembly provides sets of manifolds atboth ends of the large number of sets of horizontal pipes in a mannerthat the flow of liquid introduced to the bottom portion of the assemblypasses in a criss-cross manner from the bottom part of the assembly tothe top part of the assembly. The flow is transversely of the columnthrough several sets of horizontal pipes to a manifold and from it backto another set to another manifold from which it passes in the firsttransverse direction to a manifold above the second manifold and soforth.

This another embodiment of the heat-exchanger trays and an assembly ofthese trays is useful when the spacings between the pipes of each setare such that the trays function generally as shower-type trays. In thisembodiment the pipes of each set are staggered with respect to theadjacent set so that there is a triangularly-centered pattern. Thedistance between sets is such that the horizontal pipes of the varioussets provide surface over which the down-flowing liquid in the chamberof the column distributes itself, while the up-flowing vapors contactthat liquid. As mentioned above, the liquid flows through the pipesgenerally upwardly but in a circuitous path, that is, criss-cross path.In this embodiment downcomers and weirs are not present and the crosssection of the distillation column, at least at the elevation of theassembly of the arrays of sets of pipes, can be rectangular.

In view of the foregoing description of the heat-exchanger tray of theinvention and the assembly of heat-exchanger trays of this invention, itis apparent that the distillation column of the invention includes, asan internal, such assembly that may be located in the rectifying sectionof the column or in the stripping section of the column or such assemblycan be located in each of these sections.

As indicated above also, such assembly in the distillation column can beconstructed so that the top set of pipes feed liquid directly into thechamber of the distillation column for specific systems of the inventionusing an assembly of the heat exchanger trays. In that system the liquidfeed to the chamber of the distillation column is passed through thisassembly of heat-exchanger trays. If that system also has an assembly ofheat-exchanger trays in the rectifying section, the top and bottomheat-exchanger trays of that assembly have their inlet and outletmanifolds connected to pipes extending through the wall of the column.

In other systems of the invention the top and bottom trays of theassembly in the rectifying section or in the stripping section or inboth sections have their appropriate manifold connected to a pipeextending through the wall of the distillation column so that there isindirect heat-exchange utilization by the liquid flowing through theassembly of heat-exchanger trays in a circuitous path, while the traysfunction also as distillation trays.

The assembly of heat-exchanger trays can be used in various systems thathave the assemblies present in a number of distillation columns. Inthese systems the various systems of flow of liquid through theassemblies are such that liquid passing into and through one of theassemblies of heat-exchanger trays is fed to a second column containingone or more assemblies of heat-exchanger trays through which pass otherliquids obtained by cooling vapor effluent from the second column orobtained from other distillation columns.

The overall systems provide sufficient heat transfer utilization bythese assemblies so that tonnage requirement of refrigerant forcryogenic distillation is reduced. In such systems, as pointed outlater, the efficiency of the stages would be decreased so that thenumber of fractionation trays would be increased. However, thisadditional cost for the increased fractionation trays would be small incomparison with the savings in refrigeration costs.

DESCRIPTION OF THE DRAWINGS

In the drawings similar parts are generally designated by the samenumeral.

FIG. 1 is a horizontal cross section of a distillation column of theinvention at an elevation just above the location of the preferredembodiment of the heat-exchanger tray of the invention.

FIG. 2 is a cross section taken along the line 2--2 of FIG. 1.

FIG. 3 is an enlarged fragmentary cross section of the heat-exchangertray taken along the line 3--3 of FIG. 2.

FIG. 4 is a horizontal cross section taken along line 4--4 of FIG. 5 ofa distillation column of the invention showing another embodiment of theheat-exchanger tray of the invention in the distillation column that hasa rectangular cross section at least in its portion containing anassembly of these trays.

FIG. 5 is a fragmentary vertical cross section of the distillationcolumn of FIG. 4 showing an assembly of heat-exchanger trays of thatother embodiment.

FIG. 6 is a diagrammatic presentation of the nature of the flow ofliquid through the various assemblies of heat-exchanger trays in theassembly of these heat-exchanger trays shown in FIG. 5.

FIG. 7 is a view taken along line 7--7 of FIG. 5.

FIGS. 8, 9, 10 and 11 are schematical illustrations of various systemsof the invention containing heat-exchanger trays as assemblies invarious distillation columns of the invention.

DETAILED DESCRIPTION

FIGS. 1, 2 and 3 show a distillation column of the invention in whichthe column includes an assembly of the preferred embodiment of theheat-exchanger trays. The column is generally indicated at 12. In thesefigures only one heat-exchanger tray generally indicated at 13 iscompletely shown. The distillation column 12 has a wall 14. In view ofthe flow of liquid to, through, and from tray 13, as indicated by arrowson FIGS. 2 and 3, tray 13 is one of an assembly of these trays mountedwithin column 12 in the stripping section. That embodiment of theassembly and the other embodiment of the assembly of the invention areshown schematically in the one or more zones of various columns in FIGS.8 through 11.

The heat-exchanger tray 13, in the embodiment shown in FIGS. 1-3,includes a set of parallel horizontal pipes 15. One end of each of pipes15 is connected to a manifold pipe 16 that has holes communicating withthat open end of pipes 15. The other end of pipes 15 is connected to amanifold pipe 17. The manifold pipe 17 similarly has openingscommunicating with that other end of pipes 15. The tray 13 has avertical tube 18 that is connected to manifold pipe 17 and extendsupwardly from manifold pipe 17. The bottom open end of tube 18communicates with an upwardly facing opening 19 (FIG. 1) in the centralportion of manifold pipe 17. The manifold pipe 16 (FIG. 1) has acentrally located, downwardly facing opening 20. The trays 13 of theassembly of them are alternately disposed so that tray 13, that isimmediately above tray 13 shown in FIG. 2, is placed so that itsmanifold pipe 16 is connected to the righthand end (as viewed in FIG. 2)of its pipes 15 and its manifold pipe 17 is connected to the lefthandend (as viewed in FIG. 2) of its pipes 15. Thus tube 18 shown in FIG. 2is connected to manifold pipe 16 of the adjacent upper tray 13 so thatopening 19 of tray 13 shown in FIG. 2 communicates through tube 18 withopening 20 of the adjacent tray 13 above. Similarly, the next adjacenttray 13, that is below tray 13 shown in FIG. 2, has its tube 18connected at its top end to manifold pipe 16 at opening 20 of tray 13that is shown.

As seen in FIG. 1, heat-exchanger tray 13 in a plan view has arectangular outline and the corners of it abut cylindrical wall 14 ofcolumn 12. The pipes 15 of tray 13 are spaced from one another, asdescribed earlier, so that a pool of liquid is maintained onheat-exchanger tray 13. At two of the opposite sides of each tray 13 anexit weir 21 and an inlet weir 22 are mounted. The spacing between pipes15 is such that tray 13 is a cross-flow type of tray. Being this type oftray it also requires a downcomer (not shown) extending downwardly as adownward extension of exit weir 21. The inlet weir 22 is mounted on afixed plate 23 that extends from wall 14 to that side of tray 13. Theplate 23 prevents countercurrent flow of liquid and vapor through thisspace between tray 13 and wall 14. The ends of each of weirs 21 and 22abut wall 14 from the abutment of closed ends of manifold pipe 16 andmanifold pipe 17. The weirs 21 and 22 are spaced from adjacent pipe 15so that the distance from pipe 15 approximates the distance betweenadjacent pipes 15.

Because in the illustration tray 13 is rectangular and because wall 14is cylindrical at the elevation of an assembly of trays 13, there is aspace between portions of wall 14 and the other pair of opposite sidesof tray 13 defined by manifold pipes 16 and 17. These spaces are closedby fixed inclined plates 24 and 25, respectively. The plate 24 has itslower edge mounted on manifold pipe 16, while the lower edge of plate 25is mounted on the top of manifold pipe 17. The plates 24 and 25 preventupward passage of vapor through these spaces between pipes 15 of tray13. Preferably the fixed plates 24 and 25 are downwardly inclined tomanifold pipes 16 and 17, respectively, of tray 13, as shown, to preventaccumulation of some liquid in an area where it would remain rather thanpassing across pipes 15 from weir 22 to weir 21.

An assembly of trays 13 are shown schematically in several places inFIGS. 8-11. It is apparent from those schematic illustrations that inmost assemblies the top and bottom trays 13 differ only in one respectfrom intermediate trays 13. In most of the assemblies both top andbottom trays 13 have their manifold pipes 16 connected to a pipe thatextends through wall 14. That pipe is connected to another pipeidentified in FIGS. 8 through 11 by specific lines depending on thesystem described. The connection of such pipe would be at a centralopening like opening 20, but it can be facing wall 14 rather thanextending downwardly so that the inlet or outlet pipe, as the case maybe, can extend horizontally from manifold pipe 16 through wall 14 forthe entire length between the central portion of manifold pipe 16 andwall 14.

As seen in FIG. 8, column 12 can have two assemblies of trays 13. Oneassembly is in the rectifying section and the other assembly is in thestripping section. In the system of FIG. 8 the assembly of the trays 13in the stripping section has a top tray 13 that is merely a combinationof manifold pipe 16 and a set of pipes 15 that are shorter than those inthe other trays and that are open at the other end to introduce liquid,that has passed through the assembly, directly into the chamber ofcolumn 12. Instead of these short pipes 15 being present manifold pipe16, connected to the uppermost tube 18, can have one or more of theopenings that it would have for a connection to pipes 15, and liquidwould flow directly into the chamber from manifold pipe 16.

Referring to FIGS. 4 through 7, column 12 has, at the location ofheat-exchanger trays of this embodiment, a rectangular cross sectiondefined by a pair of opposed walls 30 and 31 and a pair of opposed walls32 and 33. Within the zone containing the assembly of heat-exchangertrays of this embodiment vertical walls 32 and 33 each provides an outerwall of a number of vertically tiered set of manifolds.

Adjacent but spaced from and parallel to walls 32 and 33 are plates 34and 35. The plates 34 and 35 extend between walls 30 and 31 of column12. One vertical margin of wall 30 and the opposed vertical margin ofwall 31 cooperate with wall 32 and plate 34 to provide a narrow chamberinside column 12 adjacent wall 32. Similarly, the other vertical marginsof walls 30 and 31 cooperate with wall 33 and plate 35 to provide aclosed chamber inside column 12 adjacent wall 33. Within the chamberbetween wall 32 and plate 34 at various elevations there are horizontalplates 36 extending from wall 31 to wall 30. Adjacent plates 36 incooperation with wall 32, plate 34 and walls 30 and 31 provide amanifold. The chamber defined by wall 33, plate 35, and walls 30 and 31has similar plates 37 to separate the chamber into a number of similarmanifolds. The elevations of plates 37 are staggered with respect to theelevations of plates 36 so that the upper portion of each manifoldbetween plates 36 is at the elevation of the lower portion of a manifoldbetween plates 37.

Horizontally across vertical plate 34 at various elevations there is aset of openings 38 and one end of a corresponding set of pipes 15 isconnected to plate 34 so that the open end of those pipes communicatewith one of the manifolds between plates 36 at those openings. A similarnumber of openings 39 are in plate 35 for communication of each of theother manifolds between plate 37 with the other end of pipes 15 mountedon plate 35. For each horizontal set of pipes 15 the spacing is suchthat in combination with the spacing between adjacent horizontal setsalong with the staggered arrangement of pipes 15 in one set vis-a-visadjacent sets, i.e., a triangularly-centered pattern, are such thatliquid in the chamber flows generally downward countercurrent toupwardly flowing vapor as described earlier for a counterflow of liquidand vapor obtained generally by the use of conventional shower-typetrays.

In this other embodiment of heat-exchanger tray, shown in FIGS. 4-7,each tray of that embodiment can be considered as including for theillustration three adjacent levels of sets of pipes 15 and the manifoldthat is connected to one end of pipes 15 of these three levels of pipes.By analogy with heat-exchanger tray 13 shown in FIGS. 1-3 it can be saidthat the manifold at each end of the three sets of pipes is betweenadjacent plates 37. The bottom portion of that manifold is equivalent tomanifold pipe 17 of the other embodiment of tray 13, while the topportion of the manifold of the embodiment of FIGS. 4-7 is generally theequivalent of tube 18. Of course, that upper portion of the manifoldbetween adjacent plates 37 also constitutes the equivalent generally ofmanifold pipe 16 for the next three upper levels of sets of pipes 15.

In most uses of the assembly described above and shown in FIGS. 4-7 thefluid to be passed through the various assemblies of heat-exchangertrays is introduced through an opening in wall 32 or wall 33. A feedpipe is connected to that plate (plate 32 or plate 33) which providesthe inlet manifold for the lowest levels of sets of pipes 15. Similarly,an outlet pipe is connected to that plate of column 12 that providespart of the construction of the final exit manifold. Of course, insteadof this exit pipe the uppermost manifold can have openings to pass thefluid, when it is a liquid feed, directly into the chamber of column 12.

In an ethylene plant light hydrocarbon feed stocks (ethane or propane)and/or heavy hydrocarbon feed stocks are pyrolytically treated toproduce a cracked gas containing hydrogen, methane, ethylene, ethane,and heavier hydrocarbons. As pointed out on page 150 of the article byA. W. Pratt et al. mentioned above, the ethylene-bearing gas from thecracking furnace is compressed in a number of stages to a substantialpressure, illustratively 600 p.s.i.g. The gas is cooled between stagesand small quantities of condensate and water are removed in interstageseparators. The gas leaving the last stage of compression is cooled bycooling water and sub-cooled by high level refrigeration to about 70° F.After removal of water and hydrocarbon condensate the cracked gas isthen passed through dehydrators to remove remaining moisture. The driedgas is then cooled to 0° F. and fed to a demethanizer distillationcolumn. The overhead from the distillation column is passed to a runbacktype condenser refrigerated by the evaporation of liquid ethylene at 5p.s.i.g. The reflux temperature shown in that article is about -130° F.From this condenser system hydrogen and methane are released to theplant fuel system, according to Pratt et al.

The embodiment of the demethanizer system shown in FIG. 8 of theattached drawings differs in several respects from the demethanizerdistillation column mentioned above and described on page 150 of thePratt et al. article. In the system of FIG. 8 the demethanizerdistillation column contains an assembly of heat-exchanger trays 13interconnected, as described earlier, in the rectifying section ofcolumn 12 instead of conventional distillation trays. Of course, therectifying section can contain conventional distillation trays above andbelow this assembly of interconnected heat-exchanger trays 13. Thecondenser 40 that receives overhead vapor from column 12 by line 41provides reflux liquid at an illustrative temperature of -145° F. to thetop point of column 12 by a line 42, while the off gas from thecondenser 40 is fed by a line 43 passing through wall 14 and connectedto a pipe connected to manifold pipe 16 of the uppermost tray 13 of theassembly in the rectifying section. The off gas, containing primarilyhydrogen and methane, passes through this assembly of trays 13 and fromthe lowermost tray 13 it passes by a pipe through wall 14 to a line 44for release to the plant fuel system or other use.

Another difference between the system disclosed in FIG. 8 and thedemethanizer system disclosed in the Pratt et al. article, is the use,in the stripping section of an assembly of interconnected heat-exchangertrays 13 instead of conventional distillation trays. In the system ofFIG. 8 that assembly is used to receive and pass through its manifoldpipes 16 and 17 and pipes 15 the feed which is the dried gas as used byPratt et al. However, the feed has not been cooled to 0° F. Instead thefeed is used illustratively at a temperature of about 50° F. to about100° F. The feed is introduced by a line 45 connected to a pipe thatpasses through wall 14 and that is connected to manifold pipe 16 ofbottom tray 13 of the assembly. The top tray 13 of this assembly in thestripping section has the construction mentioned above in which manifoldpipe 17 is absent and pipes 15 of that tray 13 are short so that thefeed is introduced from those pipes directly into the chamber. Ofcourse, the top tray 13 could be constructed conventionally inaccordance with this invention and a pipe from it could lead throughwall 14, and then back through wall 14 at a higher elevation for passingthe feed into the chamber of column 12.

In the system shown in FIG. 8 there is a reboiler generally indicated at46 but this is not a difference between the system of FIG. 8 and thedemethanization column shown by Pratt et al.

The ethylene and heavier hydrocarbons are withdrawn from the bottom ofcolumn 12 by a line 47.

In a conventional demethanizer of the prior art a very large amount ofvery-low-temperature refrigeration is required to produce a refluxhaving a temperature of about -145° F. Consequently the equipmentinvestment and operating costs are high. By using the system of theinvention in which the demethanization column is column 12 containingthe assembly of heat-exchanger trays 13 in the rectifying section of thecolumn and passing through that assembly the off gas from the condenser,there is a reduction in the amount of very-low-temperature refrigerationrequired. This is because the cold off gas, at the illustrativetemperature of -145° F., passes through trays 13 countercurrent to therising vapors in the chamber of column 12. By this indirectheat-exchange there is a transfer of thermal energy from the risingvapors to the off gases. This transfer reduces the very-low-temperaturerefrigeration requirement for condenser 40 by an equal amount of Britishthermal units (Btu).

Because the system of FIG. 8 provides for introduction of feed to bottomtray 13 of the assembly of trays 13 in the stripping section and throughthe assembly and then directly into the chamber at the top elevation ofthat assembly of trays 13, there is a countercurrent flow of feed in theassembly and liquid in the stripping section of the chamber. Due to theindirect heat exchange each Btu transferred from the feed in thatassembly of trays 13 to that liquid in the chamber in the strippingsection reduces the load on intermediate level rfrigeration equipmentfor feed by an equal amount. When the feed is introduced into theassembly in the stripping section at a temperature obtained from thedrying operation the intermediate level refrigeration is not required.

As in the case described above for the rectifying section, the strippingsection may also contain conventional distillation trays. These could bebelow the assembly of trays 13 in the stripping section. In the eventthat the feed passes from the assemblies out through wall 14 and backthrough wall 14 at level spaced some distance above the top of thatassembly for introduction to the chamber, there can be located a numberof conventional distillation trays between the point of introduction offeed to the chamber and that assembly of trays 13 in the strippingsection.

By the use of the system of FIG. 8 with the assembly of trays 13 in boththe rectifying section and the stripping section, with one utilizing offgas and the other using feed for the column, instead of a system usingconventional distillation trays in both sections as described by Prattet al., the number of trays required for both sections of the column isgreater. However, this increase in cost should be small in comparisonwith the savings in refrigertion. Of course, the system can use theassembly of trays 13 in the rectifying section with conventionaldistillation trays in the stripping section. In that case the feed wouldbe introduced by line 45 to a pipe located between the two sections andpassing into the chamber between these two sections. In that case thetemperature of the liquid feed would be conventional temperature asshown by Pratt et al.

The embodiment of the system of the invention that is shown in FIG. 9includes a demethanization distillation column 12. The system shown inFIG. 9 differs in several respects from the system shown in FIG. 8.Instead of the assembly of heat-exchanger trays 13 in the rectifyingsection using off gas from condenser 40, the rectifying section incolumn 12 of the system of FIG. 9 contains two assemblies of trays 13that are at different levels of the rectifying section. The upperassembly of these has a refrigerant passing through it that isintroduced by a line 50 and is withdrawn by a line 51. The lowerassembly of these has a refrigerant introduced by a line 52 and it iswithdrawn through a line 53.

Another difference is the introduction of feed for demethanizer column12. The line 45 introduces this feed directly into the chamber betweenthe rectifying and stripping sections. The stripping section has anassembly of heat-exchanger trays 13 connected to an inlet line 54 and anoutlet line 55. The line 54 feeds a compressed vapor that is the crackedproduct after it has been compressed as described earlier in connectionwith the overall ethylene plant but before it has been treated forremoval of hydrogen. The exit compressed vapor from this assembly passesby line 55 to a part of this system for elimination of hydrogen beforethe compressed vapor is introduced as a feed to column 12 by line 45.The manner of this elimination of hydrogen exiting by line 55 isdescribed below in connection with FIG. 10. The compressed vapor fed byline 54 can be precooled somewhat, if desired. That compressed vaporfeed in the assemby of trays 13 in the stripping section gives up someof its heat to the contents of the stripping section of the chamber andthereby substitutes in part or completely for reboiler heat. Thisreduction or elimination of reboiler heat reduces the heat load on therefrigeration system by an equal amount.

The two assemblies of trays 13 in the rectifying section with their flowof refrigerant through them transfers a considerable load oflower-temperature-level refrigeration to higher-temperature-levelrefrigeration of the overall system of the ethylene plant.

The column 12 as shown is provided with a reboiler generally indicatedat 46 as in the system of FIG. 8 but it can be eliminated in certaincases, as mentioned above.

The bottoms are removed by line 47 and the overhead is removed by line41 as described for the system of FIG. 8. The bottoms contain ethylene,ethane and heavier hydrocarbons. The overhead by line 41 is connected toa condenser system that provides a reflux to the top of the chamber ofcolumn 12 by line 42. It is noted that in this embodiment of the systemthe cold off gas from the condenser is not utilized by an assembly oftrays 13 in the rectifying section of the chamber.

The reference to the use of compressed vapor in line 54 and its passagethrough the assembly of trays 13 before it is passed by line 55 to thehydrogen eliminator is not meant to imply that all of that compressedvapor must pass through this assembly of trays 13 in column 12. Onlypart of it may be used, if desired.

Referring to FIG. 10, the system of that embodiment of the system of theinvention has demethanizer column 12 with an assembly of heat-exchangertrays 13 in the rectifying section and an assembly of heat-exchangertrays 13 in the stripping section.

The assembly of trays 13 in the rectifying section is the same as shownin the rectifying section of column 12 of the system of FIG. 8 andthrough it passes the off gas that is primarily methane introduced byline 43 and that is obtained from condenser system 40. From condensersystem 40 there is also obtained reflux liquid that is passed by line 42to the top part of the chamber of column 12. The feed to condensersystem 40 is the vapors passing overhead from column 12 and through line41. The exit off gas from this top assembly of trays 13 is removed by aline 44.

The assembly of trays 13 in the stripping section of column 12 receivesat its bottom tray 13 a feed by line 54 and the cooled feed passes outfrom the top tray 13 to line 55 that is connected to a line 56 and aline 57. From line 56 the product from line 55 passes through a heatexchanger 58, a line 59, a line 60, a heat exchanger 61, and a line 62'that feeds the product to the bottom part of a distillation column 12'.The line 57 feeds the other part of the product from line 55 through aheat exchanger 62, a line 63 and line 60 where it joins the other partof the product introduced from line 59 that provides the rest of thefeed to column 12.

Above the location of feed from line 62' the chamber of column 12'contains an assembly of heat-exchanger trays 13 that has its top trayconnected to a line 43' that receives off gas from a condenser system40'. The other product from condenser system 40' is reflux to thechamber of column 12'. That reflux is fed to the top part of the chamberby a line 42'. The overhead from column 12' is fed to condenser system40' by a line 41'.

The bottom tray 13 of the assembly in column 12' has its outletconnected to a line 64 that is connected to heat exchanger 58 forindirect heat exchange with the product from line 56 that passes throughheat exchanger 58. The off gas from line 64 after passing through heatexchanger 58 is removed by a line 65. That off gas is primarily hydrogenbut contains some methane.

The heat exchanger 61 provides indirect heat exchange with the productintroduced through line 60 to cool it by the use of a refrigerantpassing through exchanger 61 and introduced by a line 66.

The bottoms from column 12' are withdrawn by a line 67 that is connectedto exchanger 62 for indirect heat exchange with the product that isintroduced to exchanger 62 by line 57. The bottoms from line 67 aretransferred from exchanger 62 by line 45 as feed to column 12.

In the system of FIG. 10 the feed to column 12' is cooled as it passesthrough the stripping section of column 12 for the advantage mentionedabove. In addition, this feed by passing through exchangers 62 and 58 isfurther cooled so that the load requirement for cooling of feed tocolumn 12' by exchanger 61 using a refrigerant is decreased. The coolingby exchanger 58 is a utilization of the low temperature of the off gasfrom condenser system 40' that is first utilized in the assembly ofheat-exchanger trays 13 in column 12'. This is one of the means ofreducing the refrigeration requirement of exchanger 61, while the otheris the cooling by exchanger 62 that serves at the same time as a meansof raising the temperature of the feed from column 12' to column 12 byline 45. The overall system minimizes the refrigeration powerrequirement for the demethanization operation of an ethylene plant.

The demethanization operation in an ethylene plant accounts for asubstantial part of the investment of the plant. This high cost resultsfrom the very low temperatures that must be used in separating hydrogenand methane from ethylene for fractionation. Rather complicated designshave been proposed in an attempt to minimize refrigeration costs. Thesystem shown in FIG. 10 is a much simpler system than proposed by othersbut it is believed that this system is more efficient thermodynamicallyand should reduce refrigeration costs substantially. The key features ofthe system of FIG. 10 are the use of two columns, mainly, columns 12 and12' with their assemblies of heat-exchanger trays 13 and with the use ofexchangers 58 and 62 in the manner described above. The use of thecolumns avoids an inefficiency inherent in a more complicated proposeddesign mentioned above. That inefficiency results from a largetemperature gradient at the feed tray that is caused by the presence oflarge amounts of hydrogen above the feed inlet. The heat-exchanger trays13 in columns 12 and 12' recover refrigeration from the process streams.Each increment of refrigeration recovered in the rectifying section ofcolumn 12 and column 12' reduces the low-temperature-refrigerationrequirement in the condensing systems by an equal amount. Taken togetherthe two features of FIG. 10 provide for a more efficient demethanizationoperation.

The condenser systems 40 and 40' shown in the various systems of theinvention in FIGS. 8-10 can be simple refrigerated condensers butpreferably involve expansion devices. Such condensing system can be anyconventional construction.

Various specific arrangement that have been employed for the cryogenicseparation of hydrogen and methane from the ethylene and heavier gasesin the cracked gas from pyrolysis furnaces are known in the prior art.One system, after compressing the cracked gas to about 500 p.s.i. anddrying it, includes a cooling of the dried gas at this pressure to about-210° F. in three stages using first, second and third heat exchangerswith interstage flashing to remove condensate. The three condensatestreams are then fed to a demethanizer distillation column operating atabout 500 p.s.i. and with a top temperature of about -140° F. Theoff-gas stream from the third flash drum and the off-gas overhead streamfrom the demethanizer column are expanded to lower their temperatures.These off-gas streams are then passed through the third heat exchanger,the second heat exchanger and the first heat exchanger in that order.The passage of these off-gas streams is countercurrent to the passage ofgas from the second and first interstage flashing and the feed to thefirst heat exchanger in that order. In this system the demethanizercolumn uses conventional distillation trays.

Another embodiment of the system of the invention is shown in FIG. 11.That embodiment is a modification of the system described in the nextpreceding paragraph. The system of FIG. 11 differs from thatlast-mentioned system of the prior art in several respects including theuse of three assemblies of heat-exchanger trays 13 of the invention indemethanizer column 12. Another difference for the system of FIG. 11 isthe reduction of pressure of feed to demethanizer column 12 so thatcolumn 12 is operated at a pressure of less than 300 p.s.i. andillustratively 35 p.s.i.g. Instead of feeding the second condensatestream to the demethanizer distillation column in the system of FIG. 11,this second condensate stream is passed after pressure reduction throughthe intermediate assembly of trays 13 in demethanizer column 12 and thenfrom that assembly through an assembly of trays 13 in a rectifyingsection of a second condensate tower and finally directly into thattower as a feed between that assembly of trays 13 and another assemblyof trays 13 in the stripping section of that tower. The overhead fromthat second condensate tower is the feed to demethanizer column 12,instead of the second condensate that is fed directly to thedemethanizer column in the prior system.

In the system of FIG. 11 the dried cracked gas is fed by a line 70. Partof the feed in line 70 is passed from it to a line 71 that is connectedto the bottom 13 of an assembly of these trays that is in the strippingsection of a deethanizer column 12". The top tray 13 has its manifoldpipe 17 connected to a pipe extending through the wall of column 12.That pipe is connected to a line 72 to provide a part of the feed to aflash drum 73. The other part of the feed to flash drum 73 is by a line74 that receives the other part of the feed in line 70 after thatportion of the feed has passed through a first heat exchanger 75.

The second and third heat exchangers 76 and 77 constitute with firstheat exchanger 75 the three heat exchangers comparable to the heatexchangers mentioned above as being a part of the three-stage cooling inthe prior system. As in the case of that prior system both the firstheat exchanger and the second heat exchanger are provided withunnumbered inlet pipes and outlet pipes for refrigerants as shown.

The flashed vapor from drum 73, that is illustratively at the indicated515 p.s.i.g. and operated at -25° F. obtained by the cooling inexchanger 75 after prior compression of feed is passed by a line 78through second exchanger 76. A line 79 removes part of the vapor fromline 78 before it passes through exchanger 76. The flashed vapor in line79 is passed through an assembly of trays 13 in the stripping section ofdemethanizer column 12 for providing thermal energy to that section ofthe column and at the same time providing a partial refrigeration ofthat diverted part of flashed vapor that otherwise would pass throughexchanger 76 and then by a line 90 to a second flash drum 91. The drum91 is illustratively operated at essentially the same pressure as drum73. The drum 91 is at an illustrative temperature of -140° F. Thattemperature is partially achieved by the passage of flashed vapor fromline 78 through exchanger 76. The passage of another part of the flashedvapor from the first flashing stage by use of line 79 to the assembly oftrays 13 in the stripping section of column 12 partially lowers thetemperature of part of the feed that passes from that assembly of trays13 by a line 92 to second flash drum 91. Thus the refrigerationrequirement of heat exchanger 76 to obtain an overall temperature indrum 91 is substantially reduced.

The flashed vapor from second flash drum 91 is transferred by a line 93through third exchanger 77 and then by a line 94 to a third flash drum95. The flashed vapor in line 93 is cooled sufficiently in exchanger 77so that the temperature in drum 95 is illustrative -210° F. Of course,the pressure is illustratively 505 p.s.i.g. The gas flashed from drum 95is primarily hydrogen. That gas passes by a line 96 through heatexchanger 77, then by a line 97 through heat exchanger 76 and finallythrough first heat exchanger 75 after passing through a line 98. Thisgas exits from exchanger 75 by a line 99.

The condensate from drums 73, 91 and 95 exits through lines 100, 101 and102, respectively. From these lines the condensates pass throughpressure reducers 103, 104 and 105, respectively.

The condensate from drum 73, after passing through line 100 and pressurereducer 103 that reduces the pressure illustratively to 335 p.s.i.g., isintroduced by a line 106 as feed to deethanizer distillation column 12".The bottoms from second condensate tower 12' is withdrawn by a line 107and after passage through a heat exchanger 108 and a line 109 thisbottoms from second condensate tower 12' is another feed to column 12".

The bottoms from second condensate tower 12' provides a cooling of apart of the liquid withdrawn from a flash drum 110 by a line 111. Thatpart of the withdrawn liquid in line 111 passes through exchanger 108 inindirect heat exchange with the bottoms from second condensate tower 12'and passes through a line 112 and a pressure reducer 113 to a line 114.From line 114 it is fed to the stripping section of demethanizer column12.

The bottoms from deethanizer distillation column 12" are removed by aline 115. These bottoms contain propylene and heavier (higher-boiling)hydrocarbons.

The overhead from column 12" is removed by a line 116. After passagethrough a heat exchanger 117 the overhead passes by a line 118 to flashdrum 110. The flashed vapors from flash drum 110 are removed by a line119 connected to a pressure reducer 120 that is connected to a purgeline 121. The gas exiting line 121 is primarily hydrogen.

Part of the liquid removed from flash drum 110 by line 111 is returnedas reflux to the top part of the chamber of deethanizer column 12" by aline 122 connected to line 111 and to column 12". The deethanizer column12" may have conventional distillation trays (not shown) in therectifying section that is, of course, above the inlet of feed fromlines 106 and 109.

The pressure reducer 104 reduces the pressure of condensate removed fromdrum 91 by line 101 to the pressure of second condensate tower 12' thatis about the same pressure as maintained in column 12. The condensatefrom pressure reducer 104 passes through a line 125 and then through theintermediate assembly of trays 13 in column 12 that have been mentionedabove. The bottom tray 13 of that assembly is connected by a pipe to aline 126 that is connected to the inlet top tray 13 of an assembly oftrays 13 in the rectifying section of second condensate tower 12'. Thebottom outlet tray 13 of that assembly of trays 13 in the rectifyingsection of tower 12' is connected by a line 127 that introduces thiscondensate into the chamber at a lower position as feed to secondcondensate tower 12'.

As mentioned earlier, part of the flashed vapor in line 78 that comesfrom flash drum 73 passes through line 79. A part of that flashed vaporin line 79 from first flash drum 73 is passed by a line 128 to thebottom inlet tray 13 of the assembly of trays 13 in the strippingsection of second condensate tower 12', while the rest of the flashedvapor in line 79 passes, as described earlier, through the assembly oftrays 13 in the stripping section of demethanizer column 12. The topexit tray 13 of that assembly in the stripping section of secondcondensate tower 12' is connected to a line 129 that feeds this flashedvapor to line 92 for passage to flash drum 91. By this passage of stillanother part of flashed vapor from the first flash drum 73, a secondpart of flashed vapor from drum 73 is passed to flash drum 91 withoutpassage through second exchanger 76. That portion of the flashed vaporfrom drum 73 is cooled by passage through second condensate tower 12'.This further reduces the refrigeration load of heat exchanger 76.

The pressure reducer 105 reduces the third condensate withdrawn by line102 from third flash drum 95 to the low pressure in demethanizerdistillation column 12 in this embodiment of the system. That pressureis mentioned earlier. The condensate at this reduced pressure is passedfrom reducer 105 by a line 130 to the top inlet tray 13 of the assemblyof trays 13 in the rectifying section of column 12. The bottom outlettray 13 of that assembly is connected to a line 131 that introduces thiscondensate as a feed to column 12 at an elevation below that assemblyand above the intermediate assembly of trays 13 mentioned earlier as anassembly through which passes condensate from second flash drum 91 byline 101, pressure reducer 104 and line 125.

The bottoms from demethanizer distillation column 12 are removed by aline 132. These bottoms constitute primarily ethane and ethylene.

The overhead from demethanizer distillation column 12 is removed by aline 133. The overhead is primarily methane. It will contain a smallamount of hydrogen and a small amount of ethylene. From line 133 thatoverhead gas passes seriatim through third heat exchanger 77, a line134, second heat exchanger 70, a line 135, and first heat exchanger 75to an exit line 136.

In an ethylene plant one product may be a gas that is a mixture ofmethane and hydrogen. It is designed to recover from this mixture asubstantial amount of the hydrogen in the form of high-purity (95%)hydrogen. For this purpose another embodiment of the system of theinvention includes an assembly of the heat-exchanger trays mounted in aknock-back tower. The feed to the tower is first passed through a heatexchanger to lower its temperature sufficiently so that in the towerthere will be a substantial separation of hydrogen as overhead. Throughcold boxes of the heat exchanger are separately passed the overheadhigh-purity hydrogen from the tower and the methane concentrate bottomsfrom the tower. The bottoms from the tower are passed after a pressurereduction and a passage through the assembly of trays 13 located in thetower above the place of introduction of feed to the tower. The inlettray is the top tray of the assembly and the bottom tray is the outletof the assembly. From that outlet tray the methane concentrate passesthrough its cold boxes in the heat exchanger. The flow of high-purityhydrogen and the flow of methane concentrate bottoms through the heatexchanger is countercurrent to the flow of feed that then passes to thetower.

The heat-exchanger tray of the preferred embodiments of the inventiondescribed above has sets of horizontal parallel pipes and at oppositemargins of the tray there are manifolds connected to the ends of thesepipes. In light of the description of distillation trays on pages 39-55of my book mentioned above, a conventional distillation tray isprimarily a horizontal plate. In its broadest aspect the heat-exchangertray of the invention can be considered as a pair of vertically spacedplates to provide a chamber extending to opposite margins constructed asmanifolds. These plates have aligned openings for vertical passage ofvapor. In the Turbogrid tray of the prior art these openings are slotsthat extend across the intermediate portion between opposite margins.For each heat-exchanger tray of the preferred embodiments of theinvention, the margins are hollow to function a manifolds and spacedtubes are used to provide these slots and, at the same time, the chamberextending between the opposite margins of the tray of the invention is,by virtue of the use of pipes, separated into a number of parallelchambers in the intermediate portion of the tray. In these preferredembodiments the intermediate portion of the tray could be viewed as apair of corrugated plates having aligned longitudinal slots at theirjunctures where they are joined to form that number of chamberscommunicating the opposited hollow margins of the tray with each other.The walls of the tubes at an intermediate level provide those walls atthe spaces between the pipes to complete the construction of the wallsfor chambers extending between the opposite margins of the tray that arehollow to function as manifolds.

The foregoing detailed description of embodiments of heat exchangertray, the assembly of these trays, a column containing one or more ofthese assemblies and the system of the present invention have beenpresented only for purpose of illustration of these aspects of theinvention. The present invention is limited only by the claims thatfollow.

I claim:
 1. A system for the demethanization of a feed containingmethane and primarily ethylene and ethane obtained by the pyrolyticcracking of a light hydrocarbon, which comprises:a demethanizerdistillation column; conduit means to introduce said feed to saidsystem; and a condenser system to partially condense overhead vapor fromsaid column, said condenser system including:outlet conduit means toremove noncondensed vapor from said condenser system; outlet conduitmeans communicating said condenser system with the top portion of saidcolumn to provide reflux liquid from said condenser means to saidcolumn; and conduit means communicating said top of said distillationcolumn with said condenser means to transfer overhead vapor from thechamber of said column to said condenser means, said column containing:a vertical vessel; an assembly of heat-exchanger trays located in eitherthe rectifying section or the stripping section of the vessel, saidassembly of heat-exchanger trays including a number of trays, each traycomprising:a set of parallel horizontal pipes spaced from one another; afirst manifold connected to one end of each of said set of pipes having:a horizontal set of openings to provide communication between said firstmanifold and said one end of said set of pipes; and another opening forpassage of fluid into said first manifold for passage through said setof pipes from said first manifold; and a second manifold connected tothe other end of each of said set of pipes and having:a horizontal setof openings to provide communication between said second manifold andsaid other end of said set of pipes; and another opening for passage offluid out of said second manifold received from said set of pipes atsaid other end of said pipes, said spaced parallel horizontal pipes ofsaid set thereby being located at a portion of said tray between saidfirst and second manifolds and being spaced from each other so that thespacing between adjacent pipes is such that when said tray is installedand used as a distillation tray in a distillation column a pool ofdown-flowing liquid is formed above the entire area of said portion ofsaid tray between said first and second manifolds and that pool ofliquid is supported primarily on that portion of said tray by said pipeswhile up-flowing vapor can pass through said spaces between saidadjacent pipes, said assembly of heat-exchanger trays having:said traysarranged in a vertically tiered array with the set of parallelhorizontal pipes of each tray spaced from and extending parallel to theset of parallel horizontal pipes of each adjacent tray; the firstmanifold of each tray at a vertical plane passing through the secondmanifold of each adjacent tray, said vertical plane being transverse tothe longitudinal axes of the pipes of said sets of parallel horizontalpipes of said trays; and the second manifold of said each tray at avertical plane passing through the first manifold of each adjacent tray,said vertical plane being transverse to the longitudinal axes of thepipes of said sets of parallel horizontal pipes of said trays, and saidassembly further including:conduit means communicating the firstmanifold of each intermediate tray at its another opening with thesecond manifold of an adjacent intermediate tray at its another opening;conduit means communicating the second manifold of the uppermostintermediate tray at its another opening with the first manifold of theuppermost tray of the assembly at its another opening; and conduit meanscommunicating the first manifold of the lowermost intermediate tray atits another opening with the second manifold of the lowermost tray ofthe assembly at its another opening, whereby fluid passing through saidassembly flows through each set of said sets of pipes in a directionopposite to the adjacent set of said sets of pipes; first conduit meansconnected to that manifold of the lowermost tray of said assembly otherthan the manifold connected to said conduit means communicating thattray with the adjacent intermediate tray; and second conduit meansconnected to that manifold of the uppermost tray of said assembly otherthan the manifold connected to said conduit means communicating thattray with the adjacent intermediate tray, at least one of said firstconduit means and said second conduit means extending through the wallof said vessel.
 2. The system of claim 1 wherein said assembly ofheat-exchanger trays is located in the rectifying section of the vessel,both of said first conduit means and said second conduit means extendthrough the wall of said vessel and said first conduit means, thatextends through the wall of said column and is connected to saidmanifold of said lowermost tray of said assembly, is connected toconduit means providing a source of refrigerant.
 3. The system of claim2 wherein said column further includes:a second said assembly ofheat-exchanger trays located in the stripping section of the vessel;inlet conduit means for cold compressed vapor containing methane andhydrogen, said inlet conduit means extending through the wall of saidvessel and connected to that manifold of the lowermost tray of saidsecond assembly other than the manifold connected to said conduit meanscommunicating that tray with the adjacent intermediate trays; and outletconduit means extending through the wall of said vessel and connected tothat manifold of the uppermost tray of said second assembly other thanthe manifold connected to said conduit means communicating that traywith the adjacent intermediate tray.
 4. The system of claim 1 whereinsaid assembly of heat-exchanger trays is located in the rectifyingsection of the vessel, both of said first conduit means and said secondconduit means extend through the wall of the vessel and said secondconduit means, that extends through the wall of said column and isconnected to said manifold of said uppermost tray of said assembly, isconnected to said outlet conduit means to remove noncondensed vapor fromsaid condenser system to provide indirect heat transfer in therectifying section of the column from up-flowing vapor to noncondensedoverhead vapor from the condenser system with flow of said noncondensedoverhead vapor from the top part of said assembly to the bottom part ofsaid assembly before passage from the column.
 5. The system of claim 4wherein said column further includes:a second said assembly ofheat-exchanger trays located in the stripping section of the vessel; andinlet conduit means for said feed extending through the wall of saidvessel and connected to that manifold of the lowermost tray of saidsecond assembly other than the manifold connected to said conduit meanscommunicating that tray with the adjacent intermediate tray.
 6. Thesystem of claim 5 wherein said second assembly has an opening at its topfor passage of feed from said second assembly into the chamber of saidvessel of said column.
 7. The system of claim 5 and further including:asecond distillation column containing:a second vertical vessel having anoverhead outlet, a reflux liquid inlet adjacent the top of said secondvessel and a bottom outlet; and a third said assembly of heat-exchangertrays located in the vessel below said reflux liquid inlet; a secondcondenser system to partially condense overhead vapor from said secondcolumn, said second condenser system including:outlet conduit means ofsaid second condenser system to remove noncondensed vapor from saidsystem and connected to that manifold of the uppermost tray of saidthird assembly other than the manifold connected to said conduit meanscommunicating that tray with the adjacent intermediate tray; outletconduit means of said second condenser system connected to said refluxliquid inlet of said second vessel for transfer of reflux liquid fromsaid condenser system to the upper part of said second vessel; and inletconduit means connecting the overhead outlet of said second vessel tosaid second condenser system for transfer of overhead vapor from saidsecond vessel to said second condenser system; a first heat exchanger; asecond heat exchanger; a third heat exchanger; outlet conduit means forsaid second assembly of heat-exchanger trays in said stripping sectionof said first column, said outlet conduit means extending through thewall of said vessel of said first column and connected to that manifoldof the uppermost tray of said second assembly other than the manifoldconnected to said conduit means communicating that tray with theadjacent intermediate tray for removal of said feed from said secondassembly; conduit means to pass one part of said feed through said firstand third exchangers and then to the bottom portion of said secondvessel, said conduit means being connected to said second vessel and tosaid outlet conduit means connected to said second assembly in saidfirst vessel; conduit means to pass the other part of said feed throughsaid second and third exchangers and then to the bottom portion of saidsecond vessel, said conduit means being connected to said second vesseland to said outlet conduit means connected to said second assembly insaid first vessel; outlet conduit means extending through the wall ofsaid second vessel and connected to that manifold of the lowermost trayof said third assembly other than the manifold connected to said conduitmeans communicating that tray with the adjacent intermediate tray andpassing through said first heat exchanger for indirect heat transferbetween noncondensed vapor from said second condenser system afterpassage through said assembly with said one part of said feed passingfrom said second assembly to said third assembly; conduit means to passa refrigerant in indirect heat exchange relationship with both parts ofsaid feed passing through said third heat exchanger; and conduit meansconnected to said bottom outlet of said second vessel for passage ofliquid withdrawn from said second vessel through said second heatexchanger in indirect heat exchange relationship with said other part ofsaid feed and connected to said first vessel for introduction of saidwithdrawn liquid from said second column as a feed to said first columnbetween the rectifying and stripping sections.
 8. A system for theseparation of an initial product from the pyrolytic cracking of a lighthydrocarbon which contains hydrogen, methane, ethylene and ethane to anumber of products, which comprises:first, second and third heatexchangers; first, second and third flash drums; first through fifthassemblies of heat-exchanger trays, each of said assemblies ofheat-exchanger trays including a number of trays and each traycomprising:a set of parallel horizontal pipes spaced from one another; afirst manifold connected to one end of each of said set of pipes andhaving:a horizontal set of openings to provide communication betweensaid first manifold and said one end of said set of pipes; and anotheropening for passage of fluid into said first manifold for passagethrough said set of pipes from said first manifold; and a secondmanifold connected to the other end of each of said set of pipes andhaving:a horizontal set of openings to provide communication betweensaid second manifold and said other end of said set of pipes; andanother opening for passage of fluid out of said second manifoldreceived from said set of pipes at said other end of said pipes, saidspaced parallel horizontal pipes of said set thereby being located at aportion of said tray between said first and second manifolds and beingspaced from each other so that the spacing between adjacent pipes issuch that when said tray is installed and used as a distillation tray ina distillation column a pool of down-flowing liquid is formed above theentire area of said portion of said tray between said first and secondmanifolds and that pool of liquid is supported primarily on that portionof said tray by said pipes while upflowing vapor can pass through saidspaces between said adjacent pipes, each of said assembly ofheat-exchanger trays having:said trays arranged in a vertically tieredarray with the set of parallel horizontal pipes of each tray spaced fromand extending parallel to the set of parallel horizontal pipes of eachadjacent tray; the first manifold of each tray at a vertical planepassing through the second manifold of each adjacent tray, said verticalplane being transverse to the longitudinal axes of the pipes of saidsets of parallel horizontal pipes of said trays; and the second manifoldof said each tray at a vertical plane passing through the first manifoldof each adjacent tray, said vertical plane being transverse to thelongitudinal axes of the pipes of said sets of parallel horizontal pipesof said trays, and said assembly further including:conduit meanscommunicating the first manifold of each intermediate tray at itsanother opening with the second manifold of an adjacent intermediatetray at its another opening; conduit means communicating the secondmanifold of the uppermost intermediate tray at its another opening withthe first manifold of the uppermost tray of the assembly at its anotheropening; and conduit means communicating the first manifold of thelowermost intermediate tray at its another opening with the secondmanifold of the lowermost tray of the assembly at its another opening,whereby fluid passing through said assembly flows through each set ofsaid sets of pipes in a direction opposite to the adjacent set of saidsets of pipes; a demethanizer distillation column containing:a verticalvessel having an overhead outlet, first and second inlets atintermediate levels of the hight of said vessel, and a bottom outlet;and said first, second and third assemblies of heat-exchanger trayslocated in said vessel at the upper, intermediate and lower portions,respectively, of said vessel; a second distillation column containing:asecond vertical vessel having an overhead outlet and a bottom outlet;and said fourth and fifth said assemblies of heat-exchanger trayslocated in the upper and lower portions, respectively, of said secondvessel; conduit means to pass said initial product through said firstheat exchanger to said first flash drum; first pressure-reducing conduitmeans connected to said first flash drum to transfer at least a part ofits condensate to said first inlet of said demethanizer column at thezone of said third assembly as a first part of feed for saiddemethanizer column; conduit means connected to said first and secondflash drums and passing through said second heat exchanger for atransfer of a part of flashed vapor from said first flash drum to saidsecond flash drum after cooling in said second heat exchanger; conduitmeans connected to said second and third flash drums and passing throughsaid third heat exchanger for transfer of flashed vapor from said secondflash drum to third flash drum after cooling in said third heatexchanger; second pressure-reducing conduit means connected to saidsecond flash drum and to said second assembly in said vessel of saiddemethanizer column for transfer of condensate from said second flashdrum through said second assembly, said second pressure-reducing conduitmeans extending through the wall of said vessel of said demethanizercolumn and connected to that manifold of the uppermost tray of saidsecond assembly other than the manifold connected to said conduit meanscommunicating that tray with the adjacent intermediate tray; conduitmeans extending through the wall of said vessel of said demethanizercolumn and connected to that manifold of the lowermost tray of saidsecond assembly other than the manifold connected to said conduit meanscommunicating that tray with the adjacent intermediate tray andextending through the wall of said vessel of said second column andconnected to that manifold of the uppermost tray of said fourth assemblyother than the manifold connected to said conduit means communicatingthat tray with the adjacent intermediate tray; conduit means connectedto that manifold of the lowermost tray of said fourth assembly otherthan the manifold connected to said conduit means communicating thattray with the adjacent intermediate tray and open at the other end insaid second column to provide as feed to that column the condensate fromthe second flash drum after pressure reduction and passage through saidsecond and fourth assemblies; conduit means connecting said overheadoutlet of said second vessel to said second inlet of said vessel of saiddemathanizer column to provide between said second and third assembliesa second part to feed to said demethanizer column; thirdpressure-reducing conduit means connected to said third flash drum andto said first assembly of heat-exchanger trays in said demethanizercolumn, said third pressure-reducing conduit means extending through thewall of said demethanizer vessel and connected to that manifold of theuppermost tray of said first assembly other than the manifold connectedto said conduit means communicating that tray with the adjacentintermediate tray; conduit means connected to that manifold of thelowermost tray of said first assembly other than the manifold connectedto said conduit means communicating that tray with the adjacentintermediate tray and open at the other end in said demethanizer columnto provide above said second assembly a third part of the feed to saiddemethanizer column; conduit means connected to said first flash drumand said third assembly in said demethanizer column, said conduit meansreceiving another part of said flashed vapor from said first flash drumand extending through the wall of said demethanizer vessel and connectedto that manifold of the lowermost tray of said third assembly other thanthe manifold connected to said conduit means communicating that traywith the adjacent intermediate tray; conduit means connected to saidsecond flash drum, extending through the wall of said demethanizervessel and connected to that manifold of the uppermost tray of saidthird assembly other than the manifold connected to said conduit meanscommunicating that tray with the adjacent intermediate tray for transferof said another part of said flashed vapor from said first flash drum tosaid second flash drum after passage through said third assembly andwithout passage through said second heat exchanger; conduit meansextending through the wall of said second vessel and connected to thatmanifold of the lowermost tray of said fifth assembly other than themanifold connected to said conduit means communicating that tray withthe adjacent intermediate tray and connected to said first flash drum toreceive a third part of said flashed vapor from said first flash drum;conduit means extending through the wall of said second vessel andconnected to that manifold of the uppermost tray of said fifth assemblyother than the manifold connected to said conduit means communicatingthat tray with the adjacent intermediate tray and connected to saidsecond flash drum for transfer of said third part of said flashed vaporfrom said first flash drum to said second flash drum after cooling bypassage through said fifth assembly and without passage through saidsecond heat exchanger; conduit means connected to said third flash drumand passing through said third, second and first heat exchangers in thatorder to remove hydrogen from said third flash drum and to utilize it asa refrigerant in said three heat exchangers; conduit means connected tosaid overhead outlet of said demethanizer column and passing throughsaid third, second and first heat exchangers in that order to removemethane from said demethanizer column to utiize it as a refrigerant insaid three heat exchangers; means to provide refrigerant to said firstheat exchanger; and means to provide refrigerant to said second heatexchanger.
 9. The system of claim 8 for the separation of an initialproduct from pyrolytic cracking of a light hydrocarbon in which theinitial product contains propylene and higher-boiling hydrocarbons, inaddition to hydrogen, methane, ethylene and ethane, to a number ofproducts, in which:said first pressure-reducing conduit means totransfer at least a part of said condensate to said first inlet of saiddemethanizer column includes:a deethanizer distillation columncontaining a third vessel having an overhead outlet, a liquid refluxinlet at the top part of said third vessel, second and third inletslocated at an intermediate zone of said third vessel and a bottomoutlet; a pressure-reducer; a first condensate-transfer conduitconnecting said reducer with said first flash drum; a secondcondensate-transfer conduit connecting said reducer with said thirdvessel at said second inlet of that vessel to transfer condensatepassing from said first flash drum through said firstcondensate-transfer conduit and said pressure-reducer; a fourth heatexchanger; a condenser system having its inlet connected to saidoverhead outlet of said deethanizer column to partially condenseoverhead vapor from said deethanizer column, said systemincluding:outlet conduit means connected to said condenser system torecover noncondensed vapor from said condenser system; outlet conduitmeans communicating said condenser system with said reflux liquid inletof said deethanizer column to provide a part of the liquid from saidcondenser system as reflux liquid for said deethanizer column; andconduit means communicating said condenser system with said first inletof said demethanizer column through said fourth heat exchanger toprovide another part of the liquid from said condenser system as saidfirst part of feed for said demethanizer column, said system furtherincluding:conduit means communicating said bottom outlet of said secondvessel with said third inlet of said deethanizer vessel and passingthrough said fourth heat exchanger in indirect heat exchangerelationship with said another part of the liquid from said condensersystem to provide liquid from the bottom of said second vessel as a feedto said deethanizer column.
 10. The system of claim 9 wherein:saiddeethanizer column includes a sixth said assembly of heat-exchangertrays located in said third vessel below said second and third inlets ofsaid third vessel,said system further including: conduit means connectedto said first flash drum and communicating that flash drum with saidsixth assembly of heat-exchanger trays by extending through the wall ofsaid third vessel and connected to that manifold of the uppermost trayof said sixth assembly other than the manifold connected to said conduitmeans communicating that tray with the adjacent intermediate tray; andconduit means to pass a part of said initial product through said sixthassembly of heat-exchanger trays to said conduit means communicatingsixth assembly with said first flash drum, instead of through said firstheat exchanger to said first flash drum, by extending through the wallof said third vessel and connected to that manifold of the lowermosttray of said sixth assembly other than the manifold connected to saidconduit means communicating that tray with the adjacent intermediatetray.
 11. A process for the cryogenic demethanization of a feedcontaining methane and primarily ethylene and ethane obtained by thepyrolytic cracking of a light hydrocarbon, which comprises:introducingsaid feed into a vertical distillation chamber at a location between theupper rectifying section and the lower stripping section of thedistillation chamber; supporting a number of pools of liquid from thefeed at various levels in one of said sections of the distillationchamber, with the support at each level being provided primarily at anumber of spaced elongated horizontal zones by a set of spacedhorizontal chambers and with the sets of horizontal chambers at thevarious levels being interconnected at alternating ends; passing a fluidseriatim through the interconnected sets of horizontal chambers so thatthe fluid passes in opposite directions through adjacent sets ofhorizontal chambers and so that, for each level, there is a number ofhorizontal paths of travel of fluid in the same general directionthrough a set of the horizontal chambers with the fluid being inindirect heat exchange relationship with up-flowing vapor from the feedand with the supported pool of liquid that is generally flowingdownwardly through that section of the distillation chamber and with thefluid at each level passing in a direction transverse to the generaldirections of flow of the vapor and the liquid from the feed; removingfrom the top part of said distillation chamber overhead vapor containinga greater content of methane that said feed; and removing from thebottom part of said distillation chamber liquid containing a lesserconcentration of methane than in said feed.
 12. The process of claim 11wherein said section ofthe distillation chamber through which the fluidis passed is said rectifying section, said fluid is a refrigerant, andsaid flow of refrigerent is introduced at the lowermost level andwithdrawn from the uppermost level.
 13. The process of claim 11 whereinsaid section of the distillation chamber through which the fluid ispassed is said rectifying section and further including the stepsof:supporting a number of pools of liquid from the feed at variouslevels in the stripping sections of the distillation chamber, with thesupport at each level being provided primarily at a number of spacedelongated horizontal zones by a set of spaced horizontal chambers andwith the sets of horizontal chambers at the various levels beinginterconnected at alternating ends; and passing another fluid seriatimthrough the interconnected sets of horizontal chambers in the strippingsection so that said another fluid passes in opposite directions throughadjacent sets of horizontal chambers in the stripping section and sothat, for each level, there is a number of horizontal paths of travel ofsaid another fluid in the same general direction through a set of thehorizontal chambers in the stripping section with said another fluidbeing in indirect heat relationship with up-flowing vapor from the feedand with the supported pool of liquid that is generally flowingdownwardly through the stripping section of the distillation chamber andwith said another fluid at each level in the stripping section passingin a direction transverse to the general directions of flow of the vaporand the liquid from the feed,said fluid in said rectifying section beingintroduced at the uppermost level and being withdrawn from the lowermostlevel, and said flow of said another fluid in said stripping sectionbeing introduced at the lowermost level and being withdrawn from theuppermost level.
 14. The process of claim 13 wherein said fluid passedthrough said paths of travel in said rectifying section is a refrigerantand said another fluid passed through said paths of travel in saidstripping section is a compressed vapor containing methane and hydrogen.15. The process of claim 13 and further including the steps of:coolingoverhead vapor from said distillation chamber to provide a reflux liquidand a noncondensed gas; returning the reflux liquid to the top part ofsaid distillation chamber; and using the noncondensed gas as said fluidpassing through said rectifying section in the horizontal paths oftravel at the various levels.
 16. The process of claim 15 in which saidfeed is said another fluid so that before introducing said feed intosaid distillation chamber it is passed through said horizontal paths oftravel at various levels in said stripping section, said feed being at atemperature of about 50° F. to about 100° F. before passage through saidpaths of travel in said stripping section and being passed directly intosaid distillation chamber after passing through these levels in saidstripping section.
 17. A process for the cryogenic demethanization of afeed containing methane and primarily ethylene and ethane obtained bythe pyrolytic cracking of a light hydrocarbon, which comprises:passingsaid fluid seriatim through sets of spaced horizontal chambers in thestripping section of a first distillation chamber with each set ofhorizontal chambers being at different levels in the stripping sectionand with the sets being interconnected at alternating ends, each set ofspaced horizontal chambers providing at a number of spaced elongatedhorizontal zones the primary support for a pool of liquid that isgenerally flowing downwardly through the stripping section of the firstdistillation chamber, while there is up-flowing vapor between the spacedhorizontal chambers and said fluid in said horizontal chambers being inindirect heat exchange relationship with the supported pool of liquidand the up-flowing vapor with said feed at each level passing in adirection transverse to the general directions of flow of the vapor andthe liquid in the first distillation chamber; removing from thedistillation chamber said feed from said uppermost level of said pathsof flow; passing a part of said removed feed through a first heatexchange zone for cooling; passing the other part of said removed feedthrough a second heat exchange zone for cooling; passing both partsthrough a third heat exchange zone for cooling with a refrigerant;introducing said cool, removed feed into a second distillation chamber;cooling overhead vapor from said second distillation chamber to providea reflux liquid and a noncondensed gas containing primarily hydrogen;returning the reflux liquid to the top part of said second distillationchamber; passing said noncondensed gas as a fluid seriatim through setsof spaced horizontal chambers in said second distillation chamber witheach set of horizontal chambers being at different levels andinterconnected at alternating ends and each set providing primarysupport for a pool of liquid and indirect heat exchange with generallydown-flowing liquid and up-flowing vapor in the manner provided in thestripping section of the first distillation chamber but with the fluidpassing through the sets of horizontal chambers in a general directionthat is opposite to that in the stripping section of the firstdistillation chamber; withdrawing the noncondensed gas from thelowermost level of its flow in said second distillation chamber andpassing it through said first heat exchange zone for said cooling ofsaid feed; withdrawing liquid from the bottom part of said seconddistillation chamber and, after passage through said second heatexchange zone for said cooling of feed, introducing the withdrawn liquidas the actual feed to said first distillation chamber; cooling overheadvapor from said first distillation chamber to provide a reflux liquidand noncondensed gas containing primarily methane; returning the refluxliquid to the top part of said first distillation chamber; and passingthe noncondensed gas from said overhead vapor from said firstdistillation chamber seriatim through sets of spaced horizontal chambersin the rectifying section of said first distillation chamber with eachset of horizontal chambers being at different levels and interconnectedat alternating ends and each set providing primary support for a pool ofliquid and indirect heat exchange with generally downward flowing liquidand up-flowing vapor in the manner provided in the stripping section ofthe first distillation chamber but with the fluid passing through thesets of horizontal chambers in a general direction that is opposite tothat in the stripping section of the first distillation chamber.
 18. Aprocess for the cryogenic distillation to separate an initial productfrom the pyrolytic cracking of a light hyrocarbon which containshydrogen, methane, ethylene and ethane to a number of products, whichcomprises:passing said initial product at a pressure of at least about450 p.s.i.g. through a first heat exchange zone to cool it and provide apartial condensation of it; flashing the cooled product from said firstheat exchange zone to separate it into a first flasned vapor and a firstcondensate; passing a part of said first flashed vapor at the elevatedpressure through a second heat exchange zone to cool it and provide apartial condensation of it; flashing the cooled product from said secondheat exchange zone to separate it into a second flashed vapor and asecond condensate; passing said second flashed vapor at the elevatedpressure through a third exchange zone to cool it and provide a partialcondensation of it; flashing the cooled product from said third heatexchange zone to separate it into a third flashed vapor, containingprimarily hydrogen, and a third condensate; passing said third flashedvapor seriatim through said third, second and first heat exchange zonesto provide part of the cooling of said second flashed vapor, said firstflashed vapor and said initial product, respecively; passing at least apart of the components of said first condensate after a pressurereduction to a maximum pressure of about 300 p.s.i.g. to the strippingsection of a vertical demethanizer chamber; passing said secondcondensate, after pressure reduction to a maximum pressure of about 300p.s.i.g. seriatim through sets of spaced horizontal chambers in anintermediate section of said demethanizer chamber, said secondcondensate being introduced to the uppermost set of horizontal chambersand being withdrawn from the lowermost set of horizontal chambers;passing said second condensate withdrawn from said demethanizer chamberthrough sets of spaced horizontal chambers in the rectifying section ofa second vertical condensate distillation chamber and then directly asfeed into the intermediate section of that second condensate chamber;passing said third condensate, after pressure reduction to said maximumpressure, seriatim through sets of spaced horizontal chambers in therectifying section of said demethanizer chamber and then directly intosaid demethanizer chamber at a location between said rectifying sectionand said intermediate section of said demethanizer chamber; passing asecond part of said first flashed vapor at its elevated pressureseriatim through sets of spaced horizontal chambers in the strippingsection of said second condensate distillation chamber with this part ofthe first flashed vapor being introduced to the lowermost set and beingwithdrawn from the uppermost set of horizontal chambers; combining saidfirst flashed vapor, that is withdrawn from said stripping section ofsaid second condensate distillation chamber, with said one part of firstflashed vapor being flashed after its passage through said second heatexchange zone; passing a third part of said first flashed vapor seriatimthrough sets of spaced horizontal chambers in the stripping section ofsaid demethanizer chamber; combining also said third part of said firstflashed vapor with the said one part of said first flashed vapor beingflashed after its passage through said second heat exchange zone;passing overhead vapor from said second condensate chamber into saiddemethanizer chamber between said intermediate section and its strippingsection; and passing the overhead vapor, containing primarily methane,from said demethanizer chamber seriatim through said third, second andfirst heat exchange zones to provide another part of the cooling of saidsecond flashed vapor, said first flashed vapor and said initial product,respectively,with each set of horizontal chambers of the sets in thevarious vertical chambers being at different levels, interconnected atalternating ends, and providing at a number of spaced elongatedhorizontal zones the primary support for a pool of liquid that isgenerally flowing downwardly through the vertical chamber, while thereis up-flowing vapor between the spaced horizontal chambers and the fluidin the horizontal chambers being in indirect heat exchange relationshipwith the supported pool of liquid and the up-flowing vapor and with saidfluid at each level passing in a direction transverse to the generaldirection of flow of the vapor and the liquid in the vertical chamber.19. The process of claim 18 in which:the first heat exchange zone coolsthe initial feed to provide a subsequent flashing at a temperature ofabout -20° F. and the first flashing is at a pressure of about 500p.s.i.g; the second heat exchange zone cools said first flashed vapor toprovide a subsequent flashing at a temperature of about -140° F. at thatpressure; and the third heat exchange zone cools said second flashedvapor to provide a susequent flashing at a temperature of about -210° F.at that pressure.
 20. The process of claim 18 in which the initialproduct also contains propylene and higher-boiling hydrocarbons, saidprocess further including:passing another part of said initial productat said pressure seriatim through sets of spaced horizontal chambers inthe stripping section of a vertical deethanizer distillation chamberwith each set of horizontal chambers being at different levels,interconnected at alternating ends and providing at a number of spacedelongated horizontal zones the primary support for a pool of liquid thatis generally flowing downward through the stripping section of thedeethanizer distillation chamber, while there is up-flowing vaporbetween the spaced horizontal chambers and said another part of saidinitial product in the horizontal chambers being in indirect heatexchange relationship with the supported pool of liquid and up-flowingvapor, and with said another part of said initial product at each levelpassing in a direction transverse to the general direction of flow ofthe vapor and the liquid, in the deethanizer chamber; combining saidother part of said initial product from said stripping section of saiddeethanizer chamber with said part of initial product that is flashedafter passing through said first heat exchange zone; passing said firstcondensate, after pressure reduction to a pressure between about 300 andabout 350 p.s.i.g., as a feed to said deethanizer chamber; cooling theoverhead vapor from said deethanizer chamber to provide a reflux liquid;and passing at least part of said reflux liquid back to the top part ofsaid deethanizer chamber.
 21. The system of claim 20 wherein a part onlyof said reflux liquid is returned to said deethanizer chamber andfurther including:withdrawing liquid from the bottom portion of saidsecond condensate distillation chamber; passing said withdrawn liquidfrom said second condensate distillation chamber as a feed to saiddeethanizer chamber; and passing a part of said reflux liquid from saiddeethanizer chamber in indirect heat exchange with said liquid passingbetween said second condensate distillation chamber and, after pressurereduction to the pressure in the demethanizer chambe, passing it as afeed to said demethanizer chamber.
 22. The system of claim 21 in whichthe pressure reduction of the feeds to the demethanizer chamber is suchthat the chamber is operated at an elevated pressure of less than 150p.s.i. g. and the pressure reduction of the second condensate fedultimately directly into said second condensate distillation chamber isalso less than 150 p.s.i.g.
 23. The system of claim 1 wherein saidassembly of heat-exchange trays is located in the rectifying section ofthe vessel, and wherein said column further includes:a second saidassembly of heat-exchange trays located in the stripping section of thevessel; and inlet conduit means for said feed extending through the wallof said vessel and connected to that manifold of the lowermost tray ofsaid second assembly other than the manifold connected to said conduitmeans communicating that tray with the adjacent intermediate tray,saidsystem further including: a second distillation column containing:asecond vertical vessel having an overhead outlet, a reflux liquid inletadjacent the top of said second vessel and a bottom outlet; and a thirdsaid assembly of heat-assembly trays located in the vessel below saidreflux liquid inlet; a second condenser system to partially condenseoverhead vapor from said second column, said second condenser systemincluding:outlet conduit means of said second condenser system to removenoncondensed vapor from said system and connected to that manifold ofthe uppermost tray of said third assembly other than the manifoldconnected to said conduit means conmunicating that tray with theadjacent intermediate tray; outlet conduit means of said secondcondenser system connected to said reflux liquid inlet of said secondvessel for transfer of reflux liquid from said condenser system to theupper part of said second vessel; and inlet conduit means connecting theoverhead outlet of said second vessel to said second condenser systemfor transfer of overhead vapor from said second vessel to said secondcondenser system; a first heat exchanger; a second heat exchanger; athird heat exchanger; outlet conduit means for said second assembly ofheat-exchanger trays in said stripping section of said first column,said outlet conduit means extending through the wall of said vessel ofsaid first column and connected to that manifold of the uppermost trayof said second assembly other than the manifold connected to saidconduit means communicating that tray with the adjacent intermediatetray for removal of said feed from said second assembly; conduit meansto pass one part of said feed through said first and third exchangersand then to the bottom portion of said second vessel, said conduit meansbeing connected to said second vessel, said conduit means beingconnected to said second vessel and to said outlet conduit meansconnected to said second assembly in said first vessel; conduit means topass the other part of said feed through said second and thirdexchangers and then to the bottom portion of said second vessel, saidconduit means being connected to said second vessel and to said outletconduit means connected to said second assembly in said first vessel;outlet conduit means extending through the wall of said second vesseland connected to that manifold of the lowermost tray of said thirdassembly other than the manifold connected to said conduit meanscommunicating that tray with the adjacent intermediate tray and passingthrough said first heat exchanger for indirect heat transfer betweennoncondensed vapor from said second condenser system after passagethrough said assembly with said one part of said feed passing from saidsecond assembly to said third assembly; conduit means to pass arefrigerant in indirect heat exchange relationship with both parts ofsaid feed passing through said third heat exchanger; and conduit meansconnected to said bottom outlet of said second vessel for passage ofliquid withdrawn from said second vessel through said second heatexchanger in indirect heat exchange relationship with said other part ofsaid feed and connected to said first vessel for introduction of saidwithdrawn liquid from said second column as a feed to said first columnbetween the rectifying and stripping sections.